Banks said he had told the Prime Minister's office last week that he would offer his resignation if the matter was committed to trial.

"I believe the decision in the Auckland District Court was wrong and I will be contesting the charge. However I do not want this to be a distraction from the Government's programme."

Banks said he would continue to support the Government on confidence and supply votes, and would stay on as MP for Epsom and Act leader.

"My focus will now be on clearing my name and serving the people of Epsom," Banks said.

Prime Minister John Key said he had accepted Banks' offer to resign as a minister.

"Mr Banks indicated to my Chief of Staff late last week that in the event the judge ruled against him, he would tender his resignation as a Minister," Mr Key said.

If Banks was found not guilty or made a successful appeal, he would be reinstated as a minister, Mr Key said.

He said Banks' small business and regulatory reform portfolios would be reallocated this week.

Banks was committed to trial today by Judge Phil Gittos, following an oral evidence hearing in the Auckland District Court yesterday.

The charge was brought in a private prosecution by Graham McCready. Banks pleaded not guilty.

Outside court, he said he had not done anything wrong, and would continue to fight the charge.

"There are many more steps that we can take and a number of options that we can pursue, and at the moment we're looking to do that," he said.

"We believe that the decision today is wrong, and that is the advice from our legal team."

The Act Party Leader said he did not intend to step down pending the outcome of the trial.

"This is a private prosecution. This is a process. The process is long and convoluted," he said.

Prosecutor Mr McCready, who did not attend court today to hear the decision, said he was "astounded" at the win. He thought after yesterday's submissions that the case had been lost.

"I'm very pleased. It's a win for the man in the street."

Mr McCready said he intended to continue handling the prosecution himself, but would accept help from a senior lawyer. "If a lawyer steps up and says 'I'll take it over' I'll say yes, by all means, but not the Crown. The Crown has a conflict of interest."

The charge alleges Banks knowingly filed a false election return after his failed 2010 Auckland mayoral bid, listing donations from Kim Dotcom and SkyCity as anonymous when he knew who they were from.

Judge Gittos said in his decision that unchallenged evidence showed Banks knew of both donations and must therefore have known they could not properly have been recorded as anonymous.

At issue was whether Banks knew the donations were falsely recorded on the return, which he claimed not to have read.

"Minimal attention to the form would be required to see whether two $25,000 donations from Mr Dotcom's company had been correctly attributed," Judge Gittos said.

He said he was satisfied sufficient evidence had been presented to commit the defendant to trial, "and he will be committed to trial accordingly."

During an oral evidence hearing yesterday, Dotcom gave evidence of being asked by Banks to split his $50,000 donation into two $25,000 cheques, which would need to be anonymous.

SkyCity Entertainment Group CEO Nigel Morrison told the court of handing a cheque in an envelope across a table to Banks at a meeting in 2010.

A defence witness, who has name suppression, told the court he had prepared Banks' election return after his failed Auckland mayoral bid in 2010, and that Banks never read the full document.

Name suppression for the witness will lapse on Monday unless an appeal is filed. Mr Jones argued for continued suppression but Judge Gittos said electoral matters needed to be "scrupulously open."